1. Field of the Invention
The present invention relates to an inverted pendulum type vehicle capable of traveling on a floor surface.
2. Description of the Related Art
There has conventionally been known an inverted pendulum type vehicle in which a rider mounting section tiltable relative to the vertical direction is attached to a base body, to which a travel operation unit that travels on a floor surface and an actuator that drives the travel operation unit are installed. The inverted pendulum type vehicle is configured to control the traveling motion of the travel operation unit by moving the supporting point of an inverted pendulum.
In, for example, Japanese Patent Application Laid-Open No. 2011-068165 (hereinafter referred to as Patent Document 1), an inverted pendulum type vehicle in which a travel operation unit is driven according to the tilt or the like of a rider mounting section thereby to permit travel on a floor surface in all directions, including the longitudinal direction and the lateral direction relative to a rider, has been proposed by the applicant of the present application.
The conventional inverted pendulum type vehicle disclosed in Patent Document 1 enables the rider to turn the vehicle by moving his/her upper body so as to gradually change the traveling direction of the vehicle. Generally, however, the rider has been required to have a high steering skill to accomplish a smooth turn.
Especially when the vehicle is traveling forward at a low velocity or when the vehicle is almost in a stopped state, it has been difficult even for a skilled rider to turn the vehicle, i.e., to change the direction thereof.
To overcome the aforesaid shortcoming, the inventors of the present application have created a vehicle, in which an inverted pendulum type vehicle is additionally provided with an auxiliary second travel operation unit, which is separate from the aforesaid travel operation unit (hereinafter referred to as “the first travel operation unit” in some cases) and which is spaced from the first travel operation unit in the longitudinal direction. The inventors of the present application have also been engaged in the development of an art, in which, if there is a request for turning the vehicle, then the travel velocity of the first travel operation unit and the travel velocity of the second travel operation unit in the lateral direction are controlled so as to be different from each other, thereby causing the vehicle to make a turn (including a direction change).
However, various experiments and studies conducted by the inventors of the present application have revealed the following inconveniences.
In the inverted pendulum type vehicle provided with the auxiliary second travel operation unit as described above, a ground contact load acting on the second travel operation unit tends to be smaller than the ground contact load acting on the first travel operation unit. This in turn tends to cause the second travel operation unit to slip.
Meanwhile, when the vehicle is turned by controlling the travel velocities of the first travel operation unit and the second travel operation unit in the lateral direction, it is considered preferable to carry out control so as to bring an actual angular velocity of the vehicle in the yaw direction (the direction about the yaw axis) close to a desired angular velocity as much as possible.
In this case, if the magnitude of the difference between the desired angular velocity of the vehicle at the time of turning and the measured value of the actual angular velocity of the vehicle in the yaw direction is large, then excessive acceleration or deceleration of the travel velocity of the second travel operation unit in the lateral direction is apt to result. This inconveniently leads to frequent undue slip of the second travel operation unit.
An attempt to uniformly restrict the changes in the angular velocity of the vehicle regardless of the kinetic state of the vehicle in order to overcome the aforesaid inconvenience causes undue limitation to be placed on the travel velocity of the second travel operation unit in the lateral direction. This inconveniently results in impaired responsiveness of the turning behavior of the vehicle or a narrowed range of the travel velocity (the velocity in the longitudinal direction) of the vehicle that permits a smooth turning behavior.